diff --git a/pyfan.py b/pyfan.py
index 8fe1c6a..5d98edf 100644
--- a/pyfan.py
+++ b/pyfan.py
@@ -35,30 +35,34 @@ class ThermalZone:
                                                                                         self.pid.Kd)))
 
     def eval(self):
-        diff = self.target - self.get_temp()
-        val = self.pid(diff)
+        if self.get_temp():
+            diff = self.target - self.get_temp()
+            val = self.pid(diff)
 
-        try:
-            for target_fan in self.fans:
-                if type(target_fan) is dict:
-                    self.write_sysfs(list(target_fan.keys())[0], min(int(val), list(target_fan.values())[0]))
-                else:
-                    self.write_sysfs(target_fan, int(val))
-        except OSError as err:
-            logging.getLogger("pyfan").warning(
-                "[%s] Failed to set pwm, trying to reset it. (%s)" % (self.name, err.strerror))
-            self.setup_pwm(1)
+            try:
+                for target_fan in self.fans:
+                    if type(target_fan) is dict:
+                        self.write_sysfs(list(target_fan.keys())[0], min(int(val), list(target_fan.values())[0]))
+                    else:
+                        self.write_sysfs(target_fan, int(val))
+            except OSError as err:
+                logging.getLogger("pyfan").warning(
+                    "[%s] Failed to set pwm, trying to reset it. (%s)" % (self.name, err.strerror))
+                self.setup_pwm(1)
 
-        p, i, d = self.pid.components
+            p, i, d = self.pid.components
 
-        logging.getLogger("pyfan").debug(
-            "[{name}] {val}% ({diff}C/{temp}C) ({p}|{i}|{d})".format(name=self.name, val=int(val / 255 * 100),
-                                                                     diff=diff,
-                                                                     temp=self.get_temp(), p=int(p), i=int(i),
-                                                                     d=int(d)))
+            logging.getLogger("pyfan").debug(
+                "[{name}] {val}% ({diff}C/{temp}C) ({p}|{i}|{d})".format(name=self.name, val=int(val / 255 * 100),
+                                                                         diff=diff,
+                                                                         temp=self.get_temp(), p=int(p), i=int(i),
+                                                                         d=int(d)))
 
     def get_temp(self):
-        return float(self.read_sysfs(self.temp_source)) * self.factor
+        if self.read_sysfs(self.temp_source):
+            return float(self.read_sysfs(self.temp_source)) * self.factor
+        else:
+            return None
 
     def restore(self):
         self.setup_pwm(2)
@@ -94,6 +98,7 @@ class ThermalZone:
             logging.getLogger("pyfan").warning(
                 "[%s] temp source not found. Not ready yet or wrong path? (%s)" % (self.name,
                                                                                    err.strerror))
+            return None
 
     def set_pwm_mode(self, path, value=1):
         self.write_sysfs(path + "_enable", value)